1. Field of the Invention
The present invention relates generally to the antenna loops in digital tablets, and more particularly, to a layout for antenna loops in digital tablets.
2. Description of the Prior Art
Usually, a handwriting recognition system is a device with electromagnetic-induction. Conventional electromagnetic-induction devices comprise, an electromagnetic pen and a tablet. There is an oscillating circuit that consists of LC in the electromagnetic pen. If the pen point is touched, the amount of inductance will be changed, which results in a variation of oscillating frequency. The amount of inductance is increased when touching the pen point and increasing pressure so the variation of oscillating frequency is also increased. Therefore, the variation of the pressure on the pen point can be detected by way of the variation of oscillating frequency. There are two switches on the sidewall of the electromagnetic pen, the emitted frequency of the electromagnetic pen can be changed with the capacitance variation of the LC device that is produced by pushing down or setting free the switches. Furthermore, the tablet comprises a detector, an amplifier and an analog-digital converter. In the conventional tablet, there is a detected loop in the center region of the tablet, with antenna loops located on the double faces of the detecting loop, wherein the antenna loops are equidistantly arranged in order by using an array. The main purpose of the detecting loop is only applied to receive the electromagnetic wave that is emitted by the electromagnetic pen. When the electromagnetic pen emits the electromagnetic wave, the antenna loops receive the electromagnetic wave, and then the tablet can obtain correlative information by the electromagnetic induction.
In general, antenna loops and layout thereof in the conventional electromagnetic-induction device arranges antennas as check network that are distributed with equidistance in the X-direction and Y-direction of two-dimensional Cartesian coordinates to induce the electromagnetic pen and calculate the absolute position thereof. Referring to FIG. 1, it shows a layout for antenna loops distributed in the X-direction of two-dimensional Cartesian coordinates, wherein one terminal of each of the antenna loops 110A is connected to each switch (X1 to X6), whereby the reduced signal of each of the antenna loops 110A can be detected by controlling the switches X1 to X6). Because of the inverse proportion of the magnetic fields intensity to the square of distance, the electromagnetic pen that emits an electromagnetic wave is at a distance from the tablet, resulting in a weak induced signal received by antenna loops. On the contrary, the induced signal that is received by antenna loops has an increased number of intensity when the electromagnetic pen approaches the tablet. Therefore, the CPU of the tablet scans one by one and in turn each of the antenna loops to analyze intensity of induced signals that are received by each antenna loops, so as to detect the position where the cordless pen is located and calculate the coordinates thereof.
However, there is an increasing number of antenna loops in the tablet having a much larger area so a great amount of antenna switches are necessary. In a conventional method, it is necessary to notice that the distance between two adjacent logical sections in the same physical antenna loop must be adequate. If the distance is too small, it is possible to make a mis-judgment in deciding the position of the electromagnetic pen. On the other hand, nowadays, digital products are developed toward the aspect of high speeds for processing information, which is a result of electromagnetic interference. Generally, there are various digital products around the specific place for using the digital tablet. In terms of the digital tablets with bigger areas that are commercially required, the amount of switches and antenna loops in the digitizer tablets of the prior art is increased accordingly. Therefore, the method that increases amount of n-shaped sections in the same antenna loop is provided to decrease a great amount of antenna switches. Here the method increases length of the antenna loop so as to generate electromagnetic noise, that is, it is easy to be interfer with the electromagnetic noise, and that affects the calculation of the position of the pen that is located on the digital tablet. Furthermore, conventional layouts of antenna loops set limitations on scaling down the area of handwriting tablets, which results in difficulty in manufacturing panels with small boundary regions. Conventional layouts of antenna loops are formed on Printed Circuit Boards (PCB) through various semiconductor manufacturing processes (such as lithography and etch), for products with low need for high delicacy for layouts of antenna loops, such as children scribbling panels, audible books, . . . etc, although conventional layouts of antenna loops formed by the printed circuit boards process are advantageous in position detection, the cost is too high. In accordance with the above description, a new layout for multi-antenna loops in the digital tablet is therefore necessary, so as to solve the problems mentioned from the foregoing description.